Dynamisches Verhalten von Nanoclustern auf der Kupfer(111)-Oberfläche

Schlößer, D. C.

Book/Report

FZJ-2019-03395

Dynamisches Verhalten von Nanoclustern auf der Kupfer(111)-Oberfläche

Schlößer, D. C. (Corresponding author)FZJ*

1997
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Jülich : Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag, Berichte des Forschungszentrums Jülich 3475, III, 82 p. (1997)

Please use a persistent id in citations: http://hdl.handle.net/2128/22339

Report No.: Juel-3475

Abstract: The shape and the motion of ion bombardment induced monatomic deep vacancy islands on Cu(111) are studied by means of 0, variable temperature scanning tunnelling microscope (STM). The aim is to identify the atomic mechanism of vacancy island motion. After a short introduction to the problems in understanding physical phenomena taking place on nanometer scale, a detailed description of the variable temperature STM is given, which was constructed especially for this purpose. The shape of the vacancy islands with diameters of 2 - 30 nm is studied between 250 - 350 K. The island size is stable for T $\le$ 340 K on the experimental time scale. Theequilibrium shape is found to be a hexagon with corners rounding off with increasing temperature. Furthermore, shape fluctuations around the equilibrium shape canbe observed with the amplitudes of the relative fluctuation scaling non-linearly with the reciprocal island diameter. The dynamics of the coalescence of vacaney islands are discussecl and the underlying mass transport mechanism can be derived from a continuum theory based sealing model: atoms should evaporate from the island boundary and diffuse across the vacancy island (terrace diffusion). It will be shown later on that the application of the scaling model is rather problematic. At temperatures slightly above room temperature, the vacancy islands perform a lateral random motion, which can be considered as a Brownian motion. The island motionis studied as a function of island diameter and temperature by STM mmries with high time resolution. The diffusion coefficient of the vacancy islands shows a time correlation and a non-trivial scaling behaviour with both the island diameter and the temperature. From the data, an effective activation energy of 0.55 ± 0.08eV (for an island diameter d = 4.5 nm) for the rate limiting process is detennined. The activation energy increases with decreasing island diameter. The experimental results are compared to various theoretical models. It is shown t.hat single atom diffusion models based upon the assumptions of continuum theory do not yielcl an appropriate description of the experimental observations. Continuum theory is not valid for the studied structures on nanometer scale and its application leads to wrong conclusions, e.g. for the dynamic coalescence of vacancy islancls. Finally, an attempt is made to develop a collective model to explain the experimental observations.

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